1. Field of the Invention
The invention is related to measuring equipment and more particularly to instruments for measuring gap size.
2. General Background
In the nuclear industry measurement of gaps in reactor vessels, steam generators, fuel assemblies, and other related equipment is generally accomplished by the use of flat, state of the art feeler gauges. In the very thin sizes these gauges are extremely flexible. Such flexibility creates difficulty when inserting these gauges in small gaps, especially those in hard to reach places or distant locations which must be reached by attaching the gauges to remotely manipulated extension arms. Also, the method of using feeler gauges requires that a series of gauges be inserted into the gap until the most close fitting size is found. Devices using strain gauges for distance measurement which applicants are aware of include the following.
U.S. Pat. No. 4,549,355 entitled "Electronic Dendrometer" discloses the use of elongated jaws to engage a plant stem. A transducer made of flexible material spans between the jaws. A plurality of strain gauges are attached at approximate locations on the transducer and connected to a voltage source and voltmeter to monitor changes in plant stem size.
U.S. Pat. No. 4,649,752 entitled "Shime Gap Probe" discloses a probe for use in determining the thickness of an interface gap between two parts. A wave spring formed in one end of a thin elongate piece of resilient steel includes three sinusoidal waves having a peak-to-peak separation that is greater than the maximum thickness of the gaps to be measured. Strain sensors are mounted on the wave spring at the bottom of the concave depression formed by each of the sinusoids and positioned to sense the radial and circumferential strain applied to the wave spring when positioned in a gap such that the wave spring sinusoids are compressed. Two or four strain sensors may be used to create a half or full strain gauge bridge at the bottom of each concave depression. Because three strain bridges are used, information is produced that provides the two-dimensional taper as well as single dimension thickness information necessary for producing the properly sized shim to fill the gap. The shortcomings of this device are that it appears to be limited to use in relatively small gaps, it is necessary to be able to view the markings on the device to insure the device is inserted the proper distance, and it also appears that the device must be compressed before being inserted since the sinusoidal waves have a peak-to-peak separation greater than the thickness of the gap to be measured.
U.S. Pat. No. 4,622,751 entitled "Precision Electromechanical Measuring Device" discloses the use of a strain gauge or pressure transducer to sense changes of position in a workpiece contacting finger. The finger is pivotable about a relatively stiff pivot to different positions, enabling use as a center finder for circular bores and pins.
The known art does not provide for an electronic feeler gauge capable of measuring small and large gaps, that does not need to be compressed before insertion into the gap, and that provides a means for consistently insuring correct insertion depth in the gap being measured during minimum visibility conditions or remote handling operations.